A metal oxide, such as a manganese oxide, has been drawing attention as a material of diffusion barrier film (hereinafter, referred to as “barrier layer”) for preventing diffusion of metal, such as copper (Cu), from an internal metal wiring of a semiconductor device. By way of example, in Patent Document 1, there is disclosed a semiconductor device in which a manganese oxide film formed by a thermal CVD method is used as a barrier layer of a copper wiring.